This invention relates to a filter press, which is used to remove water from sludge so as to recover cake thereby obtained. Readymixed concrete to be used in a construction site is prepared through mixing in a concrete mixer truck. After it has been used, some of the readymixed concrete usually remains in the concrete mixer truck and is brought back to where the trucks are washed. Sludge is produced when separating this remaining readymade concrete into aggregate and sand, or when washing the concrete mixer truck with water. The water contained in the sludge thus produced is removed therefrom through filtration, thereby obtaining cake, which consists of cement and very fine sand. A filter press, which is used for obtaining cake from sludge through filtration, employs a number of filter plates, arranged an edge and facing each other, for the purpose of filtering out water contained in the sludge, the cake remaining on the surfaces of the filter plates. This process involves the operations of peeling the cake from the surfaces of the filter plates and, after the peeling, washing the filter cloth provided thereon with water. In view of this, a filter press requires a mechanism for separating two adjacent filter plates from each other in order to remove cake from their surfaces as well as a mechanism for washing the surface of each filter plate with water after the peeling.
The inventor of the present invention proposed a filter press structure (Japanese Patent Application No. 64-75010), according to which a number of filter plates are lodged in a frame in an arrangement in which they are set on edge and face each other. In this structure, a stationary plate is provided at one end of the frame, and a movable plate at the other end, the filter plates being set between these two plates. Provided above this frame is a horizontal track, upon which a carriage can travel. The carriage is equipped with a vertical operation cylinder, which is set in an upright position. Provided in the lower section of this vertical operation cylinder are a separating operation cylinder, which is adapted to make a telescopic movement, and a water-flow pipe, which is rotatably supported by the lower section of the vertical operation cylinder. The telescopic movement of the separating operation cylinder causes a separating rod to rotate around the axis of the water-flow pipe, thereby separating two adjacent filter plates from each other. As a result, the cake accumulated on the surfaces of these filter plates falls off. At the same time, compressed air is supplied into the above-mentioned vertical operation cylinder so as to cause it to make a telescopic movement in the vertical direction, thereby causing the above-mentioned water-flow pipe to move in the vertical direction along with the nozzles communicating with it. During this vertical movement, water is sprayed from the nozzles, thereby washing the filter cloth on the filter plates from the outside.
A problem in this filter press structure is that the filter plates are washed only from the outside, which means high-water under pressure has to be applied to them repeatedly before they can be washed clean enough to provide a high level of dewatering efficiency. As a result, the filter cloth on the filter plates do not have a long service life. In addition, this structure necessitates a very large amount of water for washing.
There is a conventional filter-cloth washing device in which the filter plates are washed solely from within. Hereafter, this mode of washing will be referred to as "reverse washing". In this device, the inlet and outlet for washing water in each filter plate have to be connected to parent water-supply and discharge pipes through flexible tubes, and water under pressure has to be supplied maintaining a certain level of uniform pressure for each filter plate. Furthermore, the mechanism for supplying water under pressure is totally unrelated to the mechanism for separating adjacent filter plates from each other in terms of its operation. As a result, a filter press equipped with both mechanisms must inevitably have a very complicated structure.